This invention is related to acoustical or ceiling panels. More specifically, this invention relates to acoustical panels that inhibit growth of fungus, bacteria and other micro-organisms.
Acoustical tiles, also known as acoustical panels, ceiling tiles or ceiling panels, are well known in the building trades for providing a ceiling that is quickly installed, inexpensive and lightweight. The tiles are prepared from a slurry of fillers and binders, most frequently by either a casting process or a felting process.
In the water felting of such a slurry, a dispersion of a filler, a binder and other ingredients flow onto a moving, porous support, such as that of a Fourdrinier or Oliver mat forming machine for dewatering. The dispersion dewaters first by gravity and then vacuum suction means. The wet basemat is dried in heated convection drying ovens and the dried material is cut to the desired dimensions and optionally top coated, such as with paint, to produce acoustical tiles and panels.
Acoustical tile is also made by a wet pulp molded or cast process such as that described in U.S. Pat. No. 1,769,519. A molding composition that includes fibers, fillers, colorants and a binder is prepared for molding or casting the body of the tile. This mixture is placed upon suitable trays which have been covered with paper or a metallic foil and then the composition is screeded to a desired thickness with a screed bar or roller. A decorative surface, such as elongated fissures, may be provided by the screed bar or roller. The trays filled with the pulp are then placed in an oven to dry or cure the composition. The dried sheets are removed from the trays and may be treated on one or both faces to provide smooth surfaces, to obtain the desired thickness and to prevent warping. The sheets are then cut into tiles of a desired size.
Use of post consumer newspaper and starch-based binders are well known to artisans and have become popular materials in acoustical tile compositions due to their low cost and environmental friendliness. However, starches and cellulosic materials also supply nutrients to growing microbes, such as bacteria, molds, mildew and fungi. As occurs with other building materials, when they become wet or are located in a very humid environment, acoustical tiles are subject to growth of microbes if nutrients are supplied. The use of paper and post consumer materials, such as recycled newspaper, not only adds to the amount of food available for microbes, but also adds to the quantity of bacteria and spores in the wet pulp already provided by airborne spores and microbes and those that may be present in the water.
Attempts have been made to reduce microbe growth by introducing biocides, such as fungicides and bacteriocides, into coatings for acoustical panels. Although some protection against microbe growth is obtained, it is short-lived under severe conditions. More effective biocides would be useful as additives to such coatings. Further, the face of an acoustical panel has openings or fissures to allow sound to be absorbed into the core. Since the coating does not penetrate the entire depth of the openings, surfaces deep in the fissures are exposed to the environment without the benefit of the protective coating unless the biocide is a migrating or leaching type. When the entire panel contains nutrients for microbes, the relatively small amount of biocide in the coating may not be sufficient to protect the larger amount of food available in the core of the panel. There is no evidence in the prior art that biocides from the coating migrate or protect the core material in any way. Even if new microbes are stopped from penetrating the core from the environment by the coating, spores and microbes in the core from the manufacturing process will begin to grow in the nutrient-rich environment if moisture is provided. Thus, coatings that include biocides have not been entirely satisfactory in inhibiting mold growth.
Some biocides are known for use in thin films and as in-can preservatives in coatings such as paints, and are known to protect the wet product and the dried film. Coatings and films that cover the surface of the acoustical panel may reduce microbe growth at the surface, but it is unknown whether the same biocides would be effective throughout the thickness of the acoustical panel. Water-insoluble species would not be expected to migrate into the core from the coating, this would leave the core unprotected.
When used in the core of the building materials, all additives have to maintain their beneficial properties through the process of forming the core. Water-soluble additive materials are likely to be washed away during the dewatering step of a felting process. In cast panels species that are relatively water-insoluble additives may not disperse adequately to be distributed throughout the entire core. Temperatures encountered during drying may be detrimental to the efficacy of the additive.
There is a need for an anti-microbial additive that protects the core of acoustical panels. The additive must be effective in reducing microbial growth after being processed with the acoustical panel and should be useful in either a felting process or a casting process. Even when the core of the panel contains nutrients that support microbial growth, the anti-bacterial additive should maintain its efficacy.